(a) Field of the Invention
The invention relates to an oviductal catalase having a molecular weight of about 60 KDa as determined by SDS-page electrophoresis under denaturing conditions and which binds to a spermatozoa membrane outer surface, uses thereof for protection and/or preservation of spermatozoa; uses thereof in artificial insemination, and a method of diagnostic of male or female infertility.
(b) Description of Prior Art
Artificial insemination (AI) has changed the face of the dairy industry. Faster genetics improvement of a herd by use of high quality bull semen is now possible, at reasonable cost, for any farmer. This is feasible by using cryopreservation by which a single bull can inseminate thousands of cows. However, during the cryopreservation process the sperm undergo several tremendous changes in cell volume. Such massive shrinkage and swelling leads to ultrastructural changes in the sperm membranes, increasing their permeability, ultimately resulting in enzyme leakage and the accumulation of intracellular calcium. Even with the best preservation techniques to date, post-thaw survival is restricted to about 50% of the sperm population. Moreover, most surviving spermatozoa have characteristics which distinguish them from spermatozoa before cryopreservation. As a consequence, the functions of cryopreserved sperm are limited, as expressed by their reduced motility, viability and fertility in vivo, which can be only partially compensated by inseminating greater numbers of live spermatozoa. In fact, to obtain a normal fertility rate, the insemination must be performed with a minimum of 6.times.10.sup.6 motile sperm per straw after thawing (.about.12.times.10.sup.6 total), compared to only 2.5.times.10.sup.6 motile fresh sperm.
Sperm quality is strongly related to free radical action and the protection provided by endogenous antioxidants. Over time, the loss of sperm motility in the rabbit and human is correlated with spontaneous lipid peroxidation (Alvarez J G et al., 1987, J. Androl., 8:338-348). It has also been reported that superoxide dismutase activity (SOD) activity is a good predictor of the lifetime of a human sperm sample (Alvarez J G et al., 1987, J. Androl., 8:338-348), and that total cellular SOD can be conveniently measured by sperm surface SOD activity. Indeed, a growing body of evidence indicates that a significant factor in human male infertility involves a loss of sperm function as a consequence of oxidative stress (Aitken R J, 1994, Reprod. Fertil. Dev., 6:19-24). Furthermore, fresh bull semen of lower quality (&lt;70% motile sperm) has lower antioxidant activity than in normal semen. However, the byproduct of SOD action is the production of hydrogen peroxide (H.sub.2 O.sub.2). Hydrogen peroxide is a highly reactive oxygen species which is one of the most toxic compound to sperm. H.sub.2 O.sub.2 could be a major player in the death of sperm in the female genital tract.
It would be highly desirable to be provided with a catalase which binds to a spermatozoa membrane outer surface to protect the spermatozoa against oxidation by H.sub.2 O.sub.2.